HI JC
As this is Interop between the managed and unmanaged worlds this is not entirely straight forward. There are a number of steps you'd need to follow to achieve this.
First up create your component in C# and register it to the Global Assembly Cache using the gacutil command line tool
Next define a COM Interface for the component, register this also.
Next create a COM Adapter for the component which implements the COM Interface.
Implement the COM Interface in your component.
Deploy the COM Adapter by regsitering to the GAC and generating a COM type library using the regasm command line tool.
Finally add the reference to the COM Adapter in your VB6 project.
There is a fair bit of documentation on this but havign only done this in training exercises rather than real world development I can't provide much more than theory.
Hope this gets you started though...
Rob
Go placidly amidst the noise and haste, and remember what peace there may be in silence - Erhmann 1927